As for a flow rate sensor detecting an intake air amount that is provided in an intake air passage of an internal combustion engine of a motor vehicle or the like, thermal sensors have conventionally been prevailing because they can directly detect a mass air quantity.
Recently, attention has been given to an air flow rate element in which after a resistor and an insulation layer film are accumulated on a silicon substrate using a semiconductor micromachining technology, a part of the silicon substrate is removed by a solvent such as KOH, and a thin film section (diaphragm) is formed, because the air flow rate element includes a high-speed responsiveness and is capable of a backward flow detection.
On the other hand, inmost cases, a semiconductor circuit element such as an LSI and a microcomputer is used in order to drive the air flow rate element by heating using a heater, where the semiconductor circuit element and the air flow rate element are directly connected at each electrode pad via a gold wire or the like or they are electrically connected to the electrode pad and a substrate wiring section via a ceramic wiring substrate that supports the semiconductor circuit element and the air flow rate element or the like.
On the other hand, recent requirements for motor vehicle components include a functional safety. With the functional safety, when, for example, any sort of abnormality occurs in sensors or actuators that make up a fuel injection system of an engine, an engine control unit (ECU) stores and detects the occurrence of the abnormality and turns on a warning indicator of an instrument panel or the like in order to let the driver know the occurrence of the abnormality, so that the driver recognizes that there is an abnormality in some part of the motor vehicle components, stops the driving of the vehicle for early repair, exchange of parts, or the like, and returns the vehicle to a safe state. This can prevent a dangerous traveling in which the driver continues a normal driving even in a state in which a motor vehicle component has an abnormality. The most important thing about the functional safety is whether each component (a sensor, for instance) diagnoses whether a current state is normal or abnormal and, if there is an abnormality, it can accurately transfer it to the ECU. In other words, it is whether a single component includes a function to output a failure signal by itself when an abnormality occurs in a part of the single component. In general, this is called a self-diagnosis function. Examples of these technologies include the one described in the patent literature 1.